Density-functional theory for the structures and thermodynamic properties of highly asymmetric electrolyte and neutral component mixtures

Density-functional theory (DFT) is applied to investigate the structural and thermodynamic properties of concentrated electrolyte and neutral component mixtures that are highly asymmetric in terms of both size and charge mimicking a crowded cellular environment. The excess Helmholtz energy functional is derived from a modified fundamental measure theory for the hard-sphere repulsion and a quadratic functional Taylor expansion for the electrostatic interactions. The direct correlation functions are obtained from the analytical solutions of the mean-spherical approximation. In the context of a primitive model where biomacromolecules are represented by neutral or charged hard spheres and the solvent is represented by a continuous dielectric medium, this DFT is able to take into account both the excluded-volume effects and the long-ranged electrostatic interactions quantitatively. The performance of the theoretical method has been tested with Monte Carlo simulation results from this work and from the literature for the pair correlation functions, excess internal energies, and osmotic coefficients for a wide variety of aqueous dispersions of charged and neutral particles.